1. Field of the Invention
The present invention relates to a novel oil-in-water emulsion containing polyethylene and particularly to sunscreen compositions, in lotion and cream form, prepared therefrom.
2. Description of Related Art
Sunscreen compositions are commonly used during outdoor work or leisure for protection of exposed skin against painful sunburn. Many effective sunscreen preparations are sold commercially or are described in cosmetic or pharmaceutical literature. In general, sunscreen preparations are formulated in the form of a cream, lotion or oil containing as the active agent an ultraviolet radiation absorbing chemical compound. The active agent acts to block the passage of erythematogenic radiation thereby preventing its penetration into the skin.
The ideal sunscreen formulation should be non-toxic and non-irritating to skin tissue and be capable of convenient application to the skin in a uniform continuous film. The product should be sufficiently stable chemically and physically so as to provide an acceptable shelf life upon storage. It is particularly desirable that the preparation should retain its protective effect over a prolonged period after application. Thus, the active agent when present on the skin must be resistant to chemical or photodegradation, to absorption through the skin, and to removal by perspiration, skin oil, or water. For aesthetic reasons, the product should be substantially odorless (or be capable of being scented) and be non-staining to the skin or clothing.
Two agents known to be effective sunscreen agents are 2-ethylhexyl-N,N-dimethyl-p-aminobenzoate (also known as octyl dimethyl, p-aminobenzoic acid ester), and 2-hydroxy-4-methoxy benzophenone (also known as oxybenzone). In addition, other para amino benzoic acid derivatives, cinnamate derivates and salicylate derivatives known to those skilled in the art are available as sunscreen agents. Each of these compounds has been employed alone, or in combination, in various sunscreen preparations.
It is known that sunscreen compositions can be formulated from emulsions. For example, U.S. Pat. No. 4,797,272 describes various microemulsions for cosmetic uses which can include conventional sunscreen agents such as those mentioned above.
It has recently been discovered that the addition of polyethylene to a sunscreen composition greatly increases its innate sun protection factor. With this new technology, polyethylene can be used as a partial substitute for conventional sunscreen agents thereby lowering production costs of sunscreen compositions. Since conventional sunscreen agents can also cause some irritation to certain people, the use of polyethylene has the further advantage of mitigating such irritation. The polyethylene technology is the subject of a commonly owned co-pending application.
U.S. Pat. No. 4,264,581 discloses a water-in-oil emulsion sunscreen composition containing polyethylene. However, a water-in-oil emulsion carrier has certain disadvantages as compared to an oil-in-water emulsion carrier. For example, oil-in-water emulsions are generally perceived as having a better feel and texture than water-in-oil emulsions. Moreover, oil-in-water water emulsions also provide a better undercoating for the subsequent application of additional cosmetics on top thereof. However, heretofore it has not been possible to formulate oil-in-water emulsions containing polyethylene since polyethylene is not stable in such emulsions.
Accordingly, it is an object of the invention to provide a stable oil-in-water emulsion which contains polyethylene.
It is a further object of the invention to provide a stable sunscreen composition in lotion and cream form formulated from an oil-in-water emulsion which contains polyethylene.
It is yet a further object of the invention to provide a sunscreen composition characterized by having a greater sun protection factor than sunscreen compositions containing the same level of sunscreen agents.